Absence of a surface-connected canalicular system in bovine platelets.

Human platelets possess a surface-connected canalicular system (SCCS) which has been postulated to subserve endocytosis as well as secretion. Platelets of most animal species studied to date, including those of cattle, function similarly. However, ultrastructural analysis of freeze-fractured bovine platelets or thin sectioned bovine platelets treated with electron-dense tracers failed to delineate a SCCS. This observation may throw an entirely new light on the role of this organelle.